The least expensive method of
determining the gradient of virtually anything is
with the use of water. Water seeks a level
automatically. One can make a water level by
attaching garden hose fittings to two (2) foot
lengths of clear plastic tubing, a male and female
fitting on opposite ends. Then each clear hose can
be attached to a common garden hose. The length of
the garden hose does not matter, nor does the
terrain in between the two ends of the hose, as
long as it is not higher in the middle than the
ends of the hose.

Erect a post at each side (or
end) of the site to be measured for elevation, and
tape or tie with string the clear plastic tubing to
each post. Make sure all connections are tight and
do not leak. Then fill the hose full of water,
letting it settle and air bubbles escape, until the
water maintains a level visible in the clear
plastic tubing. It may be necessary to raise the
lower end of the hose if water pours out, until it
too maintains a level that is both visible and
stable. If the water level fluctuates, then there
is an air leak in one of the hose connections:
tighten the connections and try it again.

Once the water level is
established, mark that spot on the post. Those
marks indicate a precise level between the posts.
You will know the height of the foundation on the
lowest corner: mark that spot on the post with a
carpenter's square. Measure between the two
marked lines on that post, write down the
measurement, and then measure down that amount on
the other post from the water mark: that
lower mark line is the top of the foundation in
that location. All four corners of a building
can be leveled in the same way, keeping one end of
the water level tied to one post.

A tight string line can be
established between the posts, and if more posts
are needed in the middle for a construction
project, the string line will indicate the level
for each one. Huge barns used to be built flat and
level using this method. But remember that while
using a water level can indicate a precise height,
it does not indicate "square"!!! You still
must measure the diagonals between corners to
establish a perfect square or rectangle.

Even canal's were surveyed in
the old days using water levels, so a water course
could be determined for running a water wheel grain
or saw mill.

This system will also work to
determine the gradient of a slope. Posts are driven
into the ground and the water level used between
them Then measure the distance from the mark to the
ground on each post is measured: the difference in
those measurements is the gradient of the slope,
but not the percentage of gradient. For that
percentage, you will need to measure the distance
between the posts and do some simple math: a 10
foot drop in 100 feet is a 10% gradient, for
example.